1. Field of the Invention
The present invention relates to a method of forming a metal line layer in a semiconductor device and, more specifically, to a method of forming a metal line layer in a semiconductor device with reliability, wherein at least one conductive layer of a plurality of conductive layers is etched, a side wall oxide film is formed on side walls of some conductive layers of the etched conductive layers, and then the other conductive layers are etched.
2. Discussion of Related Art
Now, a conventional method of forming a metal line layer in a semiconductor device will be described with reference to FIGS. 1A to 1C.
Referring to FIG. 1A, a metal line layer 110 is deposited on a lower oxide film (not shown). At that time, the metal line layer 110 can have a multilayer structure. In FIG. 1A, the metal line layer 110 has three layers 110a, 110b and 110c. Next, a photosensitive material 120 is coated thereon and patterned to open a desired portion.
Referring to FIG. 1B, the multi-layers of the metal line layer 110 are sequentially dry-etched using the patterned photosensitive material 120 as a mask. However, in the course of dry-etching the multilayered metal line layer 10, plasma ions (A, B, C) for etching go on with exhibition of various phenomena: that is, a case of linear motion (A), a case of bending due to the photosensitive material (B), and a case of ion sputtering from a bottom having been etched (C). The patterning process using plasma ions having the linear motion causes no problem, but in the patterning process using ions exhibiting the bending phenomenon and the sputtering phenomenon, side walls of the metal line layer 110 are attacked. For this reason, the reliability in the process of forming the metal line layer 110 is deteriorated.
FIG. 1C is a schematic cross-sectional view illustrating a state where the whole metal line layer 110 has been etched. When the etching process is performed up to a lowermost layer 110a of the metal line layer 110, the attacks against the side walls become serious, so that non-desired portions can be etched. In a serious case, the metal line layer may have an “I” shape, and in a more serious case, the patterns thereof may be collapsed.
Specifically, when an Al layer is used as the intermediate layer 110b, such phenomenon can occur more seriously. Further, as a width of the metal line layer 110 becomes smaller and a gap between the metal line layers becomes smaller, such phenomenon can occur more seriously. Furthermore, for the reason of problems described above, a void can be generated at a portion D when an interlayer insulating film is deposited in the subsequent process.
Therefore, measures for ensuring stability in the process of forming the metal line layer have been required.